The present invention provides a method of forming an electroluminescent circuit, and more particularly to a method of forming an electroluminescent circuit utilizing screen printing technology.
A prior art electroluminescent circuit 10 is schematically represented in crosssection in FIG. 1. This type of electroluminescent circuit consists of a substrate 20, which is typically a polyester sheet, having a plurality of interleaved first conductor segments 30 and second conductor segments 40 screen printed thereon. A dielectric layer 50 is screen printed over the interleaved conductor segments 30, 40, and a phosphor layer 60 is screen printed over the dielectric layer 50. Application of an alternating current voltage across the interleaved conductor segments 30, 40 generates a changing electric field within the phosphor layer 60, which causes the phosphor layer 60 to emit light.
FIG. 2 is a schematic representation showing a top plan-view of the interleaved conductor segments 30, 40 in the electroluminescent circuit 10 schematically represented in FIG. 1. The interleaved conductor segments 30, 40 typically have a width of 5 mils and are separated by spaces that are 5 mils in width. Due to the narrowness of the conductor segments 30, 40 and their relatively close proximity to each other, it is very difficult to produce the print screens necessary to print the interleaved conductor segments 30, 40 and/or to consistently print the interleaved conductor segments 30, 40 using the print screens. The main problems with screen printing the interleaved conductor segments 30, 40 are the formation of voids or breaks in the conductor segments 30, 40, which can result in the appearance non-illuminated areas in the electroluminescent circuit, and the formation of conductor segments that touch, which results in a short. Generally, when a short occurs in an electroluminescent circuit of this type, no portion of the circuit is illuminated.
Electroluminescent circuits of the type schematically represented in FIG. 1 are highly desirable because they can be formed using screen printing technology, they are formable and flexible because they do not contain sputtered indium tin oxide (ITO), and because they produce excellent light output at low power. However, because the average yield of satisfactory electroluminescent circuits of this type is only approximately 1% to 5% according to current fabrication methods, a new method of fabricating electroluminescent circuits by screen printing is needed.
The present invention provides a method of forming an electroluminescent circuit by screen printing. The method of the present invention comprises screen printing a rear electrode pattern on a substrate, screen printing a dielectric layer over the rear electrode pattern, screen printing a front electrode pattern on the dielectric layer, and screen printing a phosphor layer over the front electrode layer. The rear electrode pattern is preferably formed of a silver conductive ink and comprises a solid layer disposed on the substrate. The front electrode pattern is also preferably formed of a silver conductive ink and comprises a plurality of opaque lines separated by spaces. The width of the lines is preferably about 5 to about 15 mils, and the lines are preferably separated by spaces that are about 5 to about 25 mils in width. In an alternative embodiment, the method of forming an electroluminescent circuit comprises screen printing a phosphor layer on a substrate, screen printing a front electrode pattern on the phosphor layer, screen printing a dielectric layer over said front electrode pattern, and screen printing a rear electrode pattern over the dielectric layer.
The method of the present invention provides several advantages over prior art methods used to fabricate electroluminescent circuits. For example, because the electrodes are separated by a dielectric layer, there is no possibility that shorts can occur. Furthermore, even if there is a void or break in an opaque lines, or if the opaque lines touch, the electroluminescent circuit still illuminates because the lines are powered from both sides of the break or void. Thus, the yield of satisfactory electroluminescent circuits fabricated according to the method of the invention is substantially higher than the yield of satisfactory electroluminescent circuits fabricated according to conventional methods.
The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed.